Balance wheel

ABSTRACT

A balance wheel for a horological instrument comprises a substantially annular rim having an enlarged counterweight portion and carrying a body (e.g., coil, magnet). The balance wheel is designed so that the body position is normally offset from the axis of the balance wheel in order that variations in body weight cause a related movement of the balance wheel about the axis. The rotation of the axially supported and initially unpoised balance wheel presents a portion of the counterweight to a stationary tool. The counterweight portion is of a predetermined configuration and the wheel is so designed that the tool removes sufficient material to poise the balance wheel.

United States Patent 1191 1111 3,851,461 Tilse Dec. 3, 1974 [54] BALANCEWHEEL 3,626,691 12 1971 Bonsack 58/107 ,670, 92 6 1972 T k 58 28 A [75]Inventor: Wilhelm Tilse, 3 4 a amune PforzhelmBlrkenfeld Germany PrimaryExaminerEdith Simmons Jackmon [73] Assignee: Timex Corporation,Waterbury,

I [57 ABSTRACT [22] Flled: 1972 A balance wheel for a horologicalinstrument com- [21] Appl. No.: 317,850 prises a substantially annularrim having an enlarged counterweight portion and carrying a body (e.g.,coil, f Apphcat'on Data magnet). The balance wheel is designed so thatthe [63] Continuum of 42771 Feb 197! body position is normally offsetfrom the axis of the abandoned balance wheel in order that variations inbody weight cause a related movement of the balance wheel about [52]USil. 58/107, 310/36 the axis The rotation of the axially Supported and[5 I] 3/0 G04b 17/00 33/09 tially unpoised balance wheel presents aportion of the [58] Flew of Search 5 8/28 28 28 counterweight to astationary tool. The counterweight 310/36 portion is of a predeterminedconfiguration and the wheel is so designed that the tool removessufficient [56] References Cited material to poise the balance wheel.UNITED STATES PATENTS 3,524,118 8/1970 Reich 58/28 R x 5 10 DrawmgF'gures 28 s, S3 21 7 27 S15 S6 ,5:

mam 3.851.461

sum NF 2 (/35 I 1 1?, *s I S 26 s, s; 2/ j 27 5/5 I 56 23 514 S s Z4 4'[3 con.

WEIGHT Gs TORSION COIL SIDE Ms 6 -a) COUNTiWEIGHT F' 4 BALANCE WHEELThis is a continuation of application Ser. No. 114,277, filed Feb. 10,1971 which is now abandoned.

BACKGROUND OF THE INVENTION The invention relates to horologicalinstruments and more particularly to a new and improved balance wheeland method of poising same.

The prior art includes U.S. Pat. Nos. 2,745,287 and 2,554,033 which aredirected to conventional methods for poising balance wheels. Thesepatents appear to be merely of general interest and do not pertain tounsymmetrically shaped balance wheels having a coil mounted thereon.U.S. Pat. No. 3,491,530 to W. Tilse shows a typical balance wheel usedin electrical or electronic watches while U.S. Pat. Nos. 3,474,676 and3,020,682 disclose machines used for poising balance wheels. Theforegoing patents are cited as representative of the prior art and arenot intended to be all inclusive since other prior art may exist.

SUMMARY OF THE INVENTION The present invention pertains to a balancewheel carrying a body mounted thereon. The body is mountedunsymmetrically with respect to the axis of rotation of the balancewheel, that is, the center of the body is displaced a predetermineddistance from a reference plane through the balance wheel axis.Variations in body weight or wheel design, therefore, cause rotationabout the axis of the balance wheel. The rotation of the balance wheelfrom a poised position stations a particular segment of a counterweightportion of the rim in the nest of a fixed tool. Activation of the toolremoves sufficient material to cause the balance wheel to move to apoised or balanced position. The balance wheel of the present inventionmay thus be readily poised without the use of complex and expensivemachines.

Accordingly, it is an object of this invention to provide a new andimproved balance wheel.

It is another object of this invention to provide a unique method ofpoising balance wheels.

A further object of this invention is to provide a new and unobviousbalance wheel having an unsymmetrical configuration which facilitatesthe poising thereof.

A still further object of this invention is to provide an economical andexpeditious method for poising balance wheels of an unsymmetricaldesign.

Other objects and advantages of the present invention may be seen fromthe following description when viewed in conjunction with the drawingsdescribed below, where the embodiment showing a balance wheel carrying acoil is mainly used for explanation.

' DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of the balance wheelarrangement comprising the present invention;

FIGS. 2 and 3 show the position of a balance wheel having respectively alight coil and a heavy coil designed according to this invention;

FIG. 4 isa schematic related to the torsion picture of FIG. 5 and thetorsion triangle of- FIG. 6;

FIGS. 7 and 8 illustrate the conditions of maximum and minimum materialremoval;

FIG. 9 shows the amount of cut drawing where h is to be computed; and,

FIG. 10 is a sketch disclosing a balance wheel carrying magnets.

DETAILED DESCRIPTION Referring now to FIG. 1 of the drawings, thebalance wheel 10 comprises a substantially annular rim portion 11 havinga gap 12 within which part of coil 13 is mounted to the tapered faces 14and 16 of the rim 11 by means of a suitable adhesive compound 17. Theopposite side of the coil 13 is nested between the arms 18 and 19 ofyoke 21 and held in position by adhesive 22.

The yoke 21 comprises one end of a spoke 23 which extends inwardly fromthe rim ll of the balance wheel 10. The rim 11 also includes a slightlyenlarged portion 24 extending on both sides of the spoke 23 and anenlarged counterweight portion 26 having an inner curved surface 27 ofpredetermined configuration.

While the invention is depicted thusly in FIG. 1, it is to be understoodthat the balance wheel 10 could be completely annular, have a sector rimor comprise other variations thereof. Furthermore, the balance wheel 10may carry magnets as shown in FIG. 10 rather than the coil 13illustrated in the drawings. In conventional balance wheels, the spoke23 would generally be joined to the base 25 of the yoke 23 with thecenter line of the spoke 23 coinciding with the plane Y-Y through theaxis of rotation 28 and the center 35 of coil The balance wheel 10 isdesigned so that an unbalanced axially supported wheel 10 will rotate apredetermined amount with respect to a fixed tool 29, such as a punch ordrill, depending upon variations in coil weight and wheel design. Themovement of the balance wheel presents a section of the counterweight 26to the tool 29. Since the counterweight 26 decreases from a maximum insize and weight at one end to a minimum at the other end, the sectionremoved by the tool 29 is related'to the amount of rotation about theaxis 28. It is, therefore, possible to employ the same cutter or tool 29and cutting depth for different balance wheels 10. The counterweight 26and particularly the crescent shaped surface 27 thereof must bespecifically designed to accomplish this effect.

The theory of the invention is shown schematically in FIGS. 2 and 3which depict two extreme conditions. Under normal manufacturingconditions, a typical coil weight may vary fi percent, the conditionsrepresented by FIGS. 2 and 3. FIG. 2 illustrates a light coil 13 ofminimum weight which rotates the balance 10 an angle. 'y minabout theaxis 28 so that a maximum amount of counterweight material 31 is removedby the tool 29. On the other hand, the heavy coil 13 (5 percent overspecified weight) rotates the balance 10 a maximum amount, angle 'y max,with respect to the fixed tool 29 so that a minimum amount of material32 is removed. The amount of material take-off is controlled by coilposition or angle 7, due to coil weight and by the crescent shape of thecounterweight 26.

In order to design the balance wheel 10 of FIG. 1 formulas must bedeveloped for the direction of dispoise a and the amount of dispoiseM,,. Thus, FIG. 4 is a schematic representation of a portion of thebalance wheel 10 while FIG. 5 shows the various torsional forces actingon the balance wheel 10 and FIG. 6 represents the force or torsiontriangle derived therefrom.

t The tolerance 35 due chiefly to variations in coil weight is alsoillustrated in FIG. 5.

The torsional forces about the axis 28 of the balance wheel are asfollows:

Coilside: M,

G counterweight; b distance from wheel center The direction of dispoisetan a and the amount of dispoise M I may be determined by applying'thesine rule to the torsion triangle of FIG. 6 to obtain the followingrelationships:

tan a (direction of dispoise) sin B/(M,./m,,) cos B (1) M, (amount ofdispoise) M, sin B/sin a 2 The angle [3 is selected to be as small aspossible, say 1 to 10 in view of production tolerances and the distancesa and b are known for a particular balance wheel. The maximum. andminimum coil weights are substituted in the torsion formulas to obtainthe maximum and minimum torsion forces. Both the maximum and minimumangle of dispoise and amount of dispoise are then arrived at bycomputation using the respective maximum and minimum torsion values.

FIG. 7 illustrates, again in schematic fashion, the maximum amount ofmaterial to be removed from a The balance wheel 10 itself is designed bydividing the wheel into small calculable areas where s s etc., are thecenters of gravity, see FIG. 1. The sum of all torsions about the axis28, M right side, M left side, M above and M below must balance. Thewheel 10 will be balanced when the material around s is removed since inthe illustration a minimum coil weight is used. For calculationpurposes, the unknown quantities are area s (spoke) and angle 8, theangle between the centerline of the spoke 23 and the X-axis. Theunknowns, s and 8 are computed by suming the forces as follows:

EM (below) EM (above) (4) EM (left) EM (right) tan5 EM (above, below)/ZM(right, left) ventionally designed balance wheels. Using known typicalbalahce wheel 10 for poising purposes with an angle a min ofapproximately 25 while FIG. 8 illustrates a condition of minimumdispoise with an angle a max of say 88.5 and angle [3 is selected to be3. In designing the balance wheel 10, values of a and M, between the twoextremes should be calculated. Since the tool diameter and cutting depthare known the area of the material to be removed can be determined.

The crescent shaped surface 27 of the wheel 10 is arrived at bycalculating the depth of cut h for various values of M Since a fixedtool having a diameter of approximately 2 mm may be used, the amount ofmaterial take off is'determined by the curve of the balance wheel.

With reference to FIG. 9 the depth of cut h may be computed for variousvalues of M m as follows:

where F area of sector d cutting depth of sector w specific weight ofmaterial (density) Solving for M, results in the formula above whereangle 4: is unknown. Preferably using a computer, M, (amount ofdispoise) is calculated for 1 steps of angle thereby determining thecrescent shape 27 angle (ii to height h to be found in commonmathematical tables. The chord of the sector is used rather than theactual bow design of the crescent and therefore, the poising method isused sometimes only for rough poising. If there is to be a fine poisingoperation, the material take off is somewhat less than required in orderto ensure that the remaining dispoise for fine poising is still withinthe area and not on the coil side.

techniques, it is also possible to automatically feed these new-typebalance wheels 10 to a poising station at high speed therebyfacilitating the mass production process.

It is understood, of course, that the arrangements discussed above aremerely illustrative in nature. Numerous other arrangements may bereadily devised .by those skilled in the art which will embody theprinciples of the invention and fall within the spirit and scopethereof, for example designs followingthe condition of formulas (1), (2)and (4) and also formula (3) where a round tool is employed. In anotherembodiment instead of the coil 13 described above, one or more magnets40 can be used or any other body mounted on a balance wheel 41 havingweight variations. This arrangement is illustrated in FIG. 10.

-While the crescent-shaped contour 27 is positioned inside of the rim 26in the description of coil-carrying balance wheel 10, it can also belocated on the outside as shown with magnet-carrying balance wheels 41.Recess 43 and 44 are provided for balance compensation. The maximum andminimum material take offs are also illustrated in dotted lines on theouter crescent surface 42.

I claim:

1. A balance wheel comprising:

a balance body having an axis, a counterweight portion and at least oneelement subject to weight variations mounted on the other side of saidaxis from said counterweight portion to cause rotation of the bodythrough an angle when the axis is horizontal and the wheel is notproperly poised,

said counterweight portion being tapered in a peripheral direction sothat said angle is determined by the amount of dispoise, and alsovarying in distance from said axis in a predetermined manner tofacilitate removal of greater predetermined sections of saidcounterweight portion for correction of correspondingly lesser amountsof dispoise.

6 2. The combination according to claim 1, wherein therein for purposesof balance compensation and, said wheel comprises: said elementcomprises magnet means mounted in a an outer rim having saidcounterweight portion expredetermined position on said body.

tending inwardly therefrom and having a p 4. The combination accordingto claim 1, wherein mined peripheral contour, the contour of said 5 Saidbalance d comprises; counterweight portion varying to reflect conditionsof dispoise between a maximum value anda minimum value when the balancewheel is supported at its rotational axis and the location of saidcounter- Pq bemg determmixl p correspond 1 rotation thereof when thewheel is supported at its mg varlatlons in the angle of dispoise betweenprerotational axis and is not properly poise d determined limits, and

a spoke extending inwardly from the rim at a location A balance body maccordance with Clam 4 designed to balance the forces about the axis ofthe wherein: balance wheel and having an area designed to l 5 the outerrim has ring-like configuration which dlS- a balance body including anouter rim, a spoke extending inwardly from the body and having amounting yoke at the other end thereof, and

wherein said element is mounted to the yoke to cause ance said forces,said spoke terminating in a continuous forming a gap between theopposite mounting receptacle. ends l 3. The combination according toclaim 1, wherein the y Includes a mam y P0rtlon havmg a base I said bodyis substantially annular and said counterand two arms extendmg outwardlyfrom the base, weight portion is located on the outer periphery thereofa d spoke being joined to the yoke at a predeterto facilitate posing ofsaid wheel by removal of a pormined distance from the base. tion of saidcounterweight, and at least one recess

1. A balance wheel comprising: a balance body having an axis, acounterweight portion and at least one element subject to weightvariations mounted on the other side of said axis from saidcounterweight portion to cause rotation of the body through an anglewhen the axis is horizontal and the wheel is not properly poised, saidcounterweight portion being tapered in a peripheral direction so thatsaid angle is determined by the amount of dispoise, and also varying indistance from said axis in a predetermined manner to facilitate removalof greater predetermined sections of said counterweight portion forcorrection of correspondingly lesser amounts of dispoise.
 2. Thecombination according to claim 1, wherein said wheel comprises: an outerrim having said counterweight portion extending inwardly therefrom andhaving a predetermined peripheral contour, the contour of saidcounterweight portion varying to reflect conditions of dispoise betweena maximum value and a minimum value when the balance wheel is supportedat its rotational axis and the location of said counterweight portionbeing determined from corresponding variations in the angle of dispoisebetween predetermined limits, and a spoke extending inwardly from therim at a location designed to balance the forces about the axis of thebalance wheel and having an area designed to balance said forces, saidspoke terminating in a mounting receptacle.
 3. The combination accordingto claim 1, wherein said body is substantially annular and saidcounterweight portion is located on the outer periphery thereof tofacilitate posing of said wheel by removal of a portion of saidcounterweight, and at least one recess therein for purposes of balancecompensation and, said element comprises magnet means mounted in apredetermined position on said body.
 4. The combination according toclaim 1, wherein said balance body comprises: a balance body includingan outer rim, a spoke extending inwardly from the body and having amounting yoke at the other end thereof, and wherein said element ismounted to the yoke to cause rotation thereof when the wheel issuPported at its rotational axis and is not properly poised.
 5. Abalance body in accordance with claim 4 wherein: the outer rim hasring-like configuration which is discontinuous forming a gap between theopposite ends, and the yoke includes a main body portion having a baseand two arms extending outwardly from the base, said spoke being joinedto the yoke at a predetermined distance from the base.